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UC Davis Dermatology Online Journal UC Davis Dermatology Online Journal Title Quantification of ultraviolet (UV) radiation in the shade and in direct sunlight Permalink https://escholarship.org/uc/item/4wc0f6tw Journal Dermatology Online Journal, 25(7) Authors Saric-Bosanac, Suzana S Clark, Ashley K Nguyen, Victoria et al. Publication Date 2019 DOI 10.5070/D3257044801 License https://creativecommons.org/licenses/by-nc-nd/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Volume 25 Number 7| July 2019| Dermatology Online Journal || Original Article 25(7):4 Quantification of ultraviolet (UV) radiation in the shade and in direct sunlight Suzana S Saric-Bosanac1, Ashley K Clark2, Victoria Nguyen3, Adrianne Pan4, Fang-Yi Chang5, Chin-Shang Li6, Raja K Sivamani1,4,7,8 Affiliations: 1Department of Dermatology, University of California, Davis, Sacramento, California, USA, 2Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, USA, 3University of California, Davis, Davis, California, USA, 4College of Medicine, California Northstate University, Elk Grove, California, USA, 5Department of Statistics, University of California, Davis, Davis, California, USA, 6Department of Public Health Sciences, Division of Biostatistics, University of California, Davis, Sacramento, California, USA, 7Department of Biological Sciences, California State University, Sacramento, Sacramento, California, USA, 8Pacific Skin Institute, Sacramento, California, USA Corresponding Author: Raja Sivamani MD MS CAT, Department of Dermatology, University of California, Davis, 3301 C Street, Suite 1400, Sacramento, CA 95816, Tel: 916-703-5145, Email: [email protected] Introduction Abstract Exposure to ultraviolet (UV) radiation may result in Ultraviolet (UV) radiation is associated with negative sunburn, skin damage, skin cancer, premature aging, health effects, including sun damage and skin cancer. damage to the eyes, and immunosuppression [1]. The purpose of this study is to compare the Long-term exposure to UV radiation is a major factor protective effects of the shade provided by a sun leading to the development of non-melanoma skin umbrella versus that provided by a tree. Sun sensors that register the level and dose of UV radiation were cancer. Malignant melanoma, although not as placed in the shade and in direct sunlight. common as non-melanoma skin cancer, is the major Measurements were recorded every half hour cause of skin cancer related death [1]. In the United between the hours of 12:30 p.m. and 3:00 p.m. in States, since the 1970s, the incidence of melanoma Sacramento, California. The results suggest that the has increased by 4% every year and many studies level of UV radiation in the shade is not zero. The suggest that exposure to UV radiation is correlated sensors located in tree shade indicated that over 5% with the risk of developing this type of cancer [1]. In of UV radiation was detected in the shade. The order to reduce the risk of skin cancer, individuals sensors located in sun-umbrella shade showed that should minimize their exposure to UV radiation [2]. greater than 17% of UV radiation reached the shade. When outdoors, the appropriate sun protective The sun sensors used in our study collected UV measures should be taken, including wearing sun radiation data relevant to UV index; however, they protective clothing, applying sunscreen, wearing did not differentiate between UVA, UVB, visible, and sunglasses, and staying in the shade when possible. infrared light. The amount of UV radiation detected in the shade is not zero, thus regular sunscreen use There are two forms of radiation caused by sunlight: and other sun protective practices should be direct radiation and diffuse radiation. Tree shade and followed to reduce the risk of sun damage and skin hats, for example, may protect the skin from direct cancer. radiation by blocking sunlight from reaching the skin. However, diffuse radiation may come from all directions and protective measures may not be as Keywords: ultraviolet, UV, radiation, skin cancer, sunlight, effective. For example, in tree shade there may be shade less direct radiation compared to that in direct - 1 - Volume 25 Number 7| July 2019| Dermatology Online Journal || Original Article 25(7):4 sunlight, because trees are able to filter the direct accumulated UV dose according to the formula: component. A larger proportion of UV dose in the Dose = UVI × time (hours). The sun sensors also shade comes from diffuse radiation. provide a measurement of the UV level, which is an Even though diffuse radiation can be detected in the approximate measure of the theoretical UVI. Table 1 shade, utilization of shade is believed to be one shows how the theoretical UVI is related to the UV important strategy to minimize UV exposure and level measured by the sun sensors. protect the skin from UV damage [2]. A study of 50 The level display changes quickly depending on trees in Australia showed that the erythemal UV in direct sunlight exposure, whereas the dose reflects the shade depended on the tree canopy density and the cumulative UV exposure. The sun sensors were the height of the start of canopy above the ground, used to measure UV dose and level in the shade and with no significant dependence on canopy width or in direct sunlight. To further assess the role of shade, tree height [3]. Additionally, Parisi et al. showed that measurements were recorded under tree shade and on a summer afternoon, 61% of erythemal UV sun umbrella shade. radiation in tree shade was related to diffuse UV level and dose next to swimming pool component of UV [4]. Moreover, about 56% of Two swimming pools, one located in Davis, California ultraviolet radiation type A (UVA) radiation is due to (latitude 38.5) and the other in Sacramento, a diffuse component [4]. These values are similar to California (latitude 38.6) were used for data the percentage of diffuse UV radiation detected in collection. The measurements of UV dose and level full sun on a winter afternoon (diffuse erythemal UV, occurred at 30-minute intervals at the following 46%; diffuse UVA, 28%). The higher diffuse UV times (Pacific Standard Time): 12:30 p.m., 1:00 p.m., radiation in the summer tree shade may result in 1:30 p.m., 2:00 p.m., 2:30 p.m., and 3:00 p.m. The high UV exposure of skin and other parts of the body, measurements were done on a horizontal plane at including the eyes. Moreover, hats may provide more ground level in the shade that was provided by a protection from direct radiation than from diffuse sun-umbrella, as well as in direct sunlight (Figure 1). radiation [4]. The distance between coin dosimeters in the shade Quantitative measurements of UV radiation in and those in direct sunlight was approximately 12 various environments are needed for developing meters. The measurements were recorded on the optimal sun protection strategies. Although there same days at both locations. The theoretical UVI and have been numerous studies on quantifying UV the ambient temperature were the same at the two radiation in tree shade, few studies quantify UV locations, thus both locations were combined for the exposure in the shade near a swimming pool, a purposes of data analysis. At each time point, there potentially reflective surface. In this study, our were ten sensors in the shade (provided by the sun- primary objective was to quantify the UV exposure in umbrellas) and ten in direct sunlight, next to the direct sunlight by a swimming pool compared to the pool. The coin dosimeters used for data collection in UV exposure in the shade by a swimming pool direct sunlight were placed at a distance of one (shade provided by sun-umbrella). meter from the pool. All data were recorded on three sunny days in September 2016. Methods Table 1. UV Level Displays in Sun Sensor. Measurement of UV level and dose Number of “Level” Corresponding Intensity of bars displayed on theoretical UV UV measurements were conducted with a SunSense sunlight Coin®, which were kindly donated from SunSense sun sensor Index 1 Low 1-2 company (Norway). The sun sensors register 2 Moderate 3-5 erythema-weighted ultraviolet (UV) radiation 3 Strong 6-7 according to the international UV index (UVI). From 4 Very strong 8-10 the time the coin is turned on, it displays the 5 Extreme 11+ - 2 - Volume 25 Number 7| July 2019| Dermatology Online Journal || Original Article 25(7):4 and dose were measured on a horizontal plane at ground level in the tree shade and adjacent full sunlight using the sun sensors. The coins were moved throughout the day to maintain exposure to the sun, but they remained at an approximately equal distance from the tree trunk at all times (approximately 15 meters). The dosimeters that were recording data in the shade remained next to the tree trunk at all times. For each of the two trees, five coin dosimeters were collecting data in direct sunlight while five were in the shade, next to the tree trunk. Thus, at each time point, there were collectively ten measurements in the sun and ten in the shade. The data from the two trees were combined for the purposes of analysis as data collections were done on the same days, at the same times, at the same latitude. All data were recorded on three sunny days in September and October 2016. Statistical methods Since the UV dose is a continuous outcome variable, a linear mix-effects model was used to fit the Figure 1. The overall experimental setup, showing sun sensors in repeated measures UV dose data over time (12:30 tree shade (top panel) and sun umbrella shade (bottom panel). p.m. to 3:00 p.m.) to estimate the change rate in the UV dose for each of the two locations, direct sunlight UV level and dose next to tree and shade, and compare their change rate in the UV In Sacramento, California (latitude 38.6), two trees dose over time.
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